The global clock can be used in many fields. Only when the synchronization of global clocks of independent systems is achieved such that the clock of each independent system arrives at a standardized clock reference, the array of these systems can work in cooperation, to ensure there is a consistent measurement condition between systems. It thus is necessary to provide a method for determining an inter-system global clock.
At present, in order to determine an inter-system global clock, a time-stamp communication between multiple systems is generally used to acquire clock references for clocks of these systems, and such clock references are further used for calibration. This way has been widely used in the field of communication. Although this synchronizing method allows the time synchronization between systems, it is limited to use existing communication protocols, which enables the time reference to be packaged into a time stamp, to achieve a global clock synchronization of low precision, for example, in milliseconds, sub-milliseconds, microseconds, or sub-microseconds. The precision in such a way ultimately depends on a clock speed, i.e., flipping frequency, so it does not arrive at a synchronization precision shorten than the clock cycle. A consistent time reference is generally required among multiple independent systems to satisfy an accurate time measurement in some application fields, such as nuclear detection, or time of flight. A completely synchronized global clock has a high requirement for precision, which is required to a range from nanoseconds to picoseconds, and generally smaller than the clock cycle of the system clock. The arrangement of the global clock should consider the slight difference caused by the different orders in which the respective clocks of the systems are powered on, but the traditional methods fail to meet the requirement.